1. Field of the Invention
The invention relates to a device for harmonization between a laser emission path and a passive observation path, the optical paths having axes that may be separate or the same. The harmonizing consists in making the optical axes of these paths parallel so that they have a common line of sight. The invention can be applied especially to target designation systems comprising a laser path and a passive observation path or the imager or offset measurement device type. It can be applied also to active/passive imaging systems comprising a scanning laser emission path and a passive imaging path. More generally, it can be applied to any system where the laser emission path and the passive observation path have to be harmonized.
2. Description of the Prior Art
In harsh environmental conditions, especially in terms of temperature and vibration, target designation by laser is advantageously done by means of a &lt;&lt;pod &gt;&gt; arranged for external carriage in the aircraft. It may have an imaging path with band II or band III infrared detection, enabling the location of a target and a laser path whose optical axis may be separate or the same as that of the imaging path. This laser path has emission for example in the near infrared and is `locked` into the imaging path. This locking implies perfect "alignment" between the two paths. In other words, it implies perfect parallelism between their optical axes (whether or not these axes are one and the same axis). These optical axes then define one and the same line of sight. It should be possible to monitor this harmonizing during a mission.
If the emission wavelength of the laser is not included in the spectral band of the sensor of the imaging path or if the laser should send pulses that are too short to be detected by the sensor, it is not possible to harmonize the paths by taking a fraction of the laser beam and reflecting it to the sensor in order to determine the offset between the spot formed by the laser on the sensor and the center of the sensor.
The French patent application No. 2 669427 describes a device to monitor the alignment of a laser beam sighting path and an infrared imaging path, for example in a laser designation pod. This device consists of a housing comprising a cassette containing a polyimide film and means for advancing this film. During the harmonizing procedure, the laser beam is focused on the film which gets heated up, thus generating a hot point displayed on the infrared detector. This enables a measurement of the alignment offset between the two paths. In order to be visible in the band II or III, the heating must be substantial and lead to the local destruction of the film. This explains the film advancing means that have been installed. The housing is bulky and the solution described does not enable the harmonizing to be done during the operations of designation. Nor does it permit the harmonizing to be done for operational lines of sight, especially when the system provides for a possible deflection of the line of sight.
The device according to the invention overcomes these drawbacks by implementing means of conversion by which it is possible, for example from a fraction of the incident laser beam, to obtain a beam that is detectable by the detector of the passive path. These means are based on the photoluminescence properties of certain materials.